A longitudinal study of the effects of the birth of a sibling during the first 6 years of life

We investigate links among the birth of a new infant, changes in the family environment, changes in the relationship between the mother and an older child, and changes in an older child's cognitive and socioemotional development We hypothesize that the effects of sibling birth are mediated by the associated changes in the family environment and changes in the interaction patterns of the family members. Data from the National Longitudinal Survey of Youth are used on a cohort of nonminority children between 6 and 23 months old. The birth of a sibling results in significant changes in the family environment. At the same time, positive interactions with the older child diminish, especially if the birth interval is short, and the mother increasingly adopts controlling parenting styles. These changes result in lower levels of verbal development. About 2.5 years after the sibling birth, negative effects are detected on achievement and on socioemotional adjustment. Some positive effects of sibling birth also are noted on verbal ability and peer relations.